(2-o-Chlorophenyl)-2-methylamino-cyclohexanone (ketamine) is an effective non-opioid anaesthetic/analgesic drug [Laskowski et al., Can J Anesth 2011, 58, 911: Carstensen & Møller, Br J Anaesth. 2010, 104, 401], with the major advantages over opioids in that it shows no respiratory depression or hyperalgesic effects, and is also free of longer-term effects such as increased tolerance and immune suppression.
Ketamine is normally used as the racemate, but more recently the more active (S)-enantiomer has begun to be employed. (S)-Ketamine has similar pharmacological, analgesic and anaesthetic properties to the racemate, but is about twice as potent [Adams & Werner, Anaesthetist 1997, 46, 1026].

The most important adverse effect of ketamine is its hallucinogenic properties which, together with its relatively long half-life (2-3 h) means that it is normally administered together with sedative or hypnotic drugs like midazolam and/or propofol to control the prolonged period of post-anesthesia hallucinations [Domino, Anesthesiology 2010, 113, 678, Chiaretti et al., Pediatric Blood & Cancer 2011, 57, 1163]. While (S)-ketamine has somewhat faster elimination [Adams & Werner, Anaesthetist 1997, 46, 1026], there is still a need for analogues with much shorter half-lives to avoid the concomitant use of sedatives/hypnotics.
It is an object of the present invention to go some way to meeting this need, and/or to at least provide the public with a useful choice.
Other objects of the invention may become apparent from the following description which is given by way of example only.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date.